1. Field of the Invention
The present invention relates to an optical disc apparatus for reading information recorded on an optical disc medium such as a CD, a DVD, and a Blu-ray Disc™, a method of controlling the optical disc apparatus, and an information storage medium.
2. Description of the Related Art
In recent years, various types of optical disc media have been used as information recording media. In general, the optical disc medium has a structure in which a plurality of layers such as a data recording layer for recording information thereon and a protective layer for protecting the data recording layer are laminated. In order to read the information recorded on such an optical disc medium, an optical disc apparatus is used. The optical disc apparatus includes an optical pickup for irradiating the optical disc medium with light to detect light reflected from the optical disc medium.
When the optical disc apparatus reads the information recorded on the optical disc medium, it is necessary to adjust a focus of an objective lens included in the optical pickup to be on a signal surface (surface of the data recording layer) of the optical disc medium. Therefore, when the information is read, the optical disc apparatus performs a focus detection operation for detecting a focus state where the focus of the objective lens is on the signal surface based on an output signal from the optical pickup (for example, see Japanese Patent Application Laid-open No. 2007-052896). Specifically, the optical disc apparatus judges whether or not the output signal from the optical pickup satisfies a predetermined detection condition while relatively moving the objective lens of the optical pickup with respect to a surface of the optical disc medium (medium surface). Then, when the output signal satisfies the predetermined detection condition, the optical disc apparatus judges that the focus of the objective lens is on the signal surface.